Process for producing crinkled plastic ribbon

ABSTRACT

The present invention relates to a process for making a flatextruded yarn or ribbon of melt-extrudable thermoplastic material having a characteristic surface configuration, and to a method and apparatus for producing such yarn or ribbon.

Unlted States Patent 1191 1111 3,715,422 Chopra et al. 1 51 Feb. 6, 1973154] PROCESS FOR PRODUCING [56] References Cited LRINKLED PLASTlC R'BBONUNITED STATES PATENTS [75] [Inventors-Z Sohmd" f E Hawkesbu' 2,816,34912/1957 Pamm 6121].. ,.264/177 F ry, Quebec, llllalre Marcel Turmel, 2748 4 [1958 Fmlayson et al. ..264/177 F Quebec both f 3 219 739 11/1965Breen et al. ..264/177 F Canada 3:266:093 8/1966 Corbett ..18/14 3Assigneez Chemical Limited, Montreal 3,354,250 1 H1967 v Killoran etal.". ..264/176 F Quebec 3333? 5/1333 331132523111? "56 43142 1 [22]Filed: May 18, 1970- 314913405 1/1970 Palmer el al. ..264/176 F3,562,369 2 1971 cm 1'21 61 1. ..264/210 R [211 P 48,752 3,283,37811/1966 crar rlpton ..264/210 R 3,002,804 1961 Kilian ......264/l78 FRelated '5' Apphcam Dam 3,259,938 7/1966 Martin ..18/8 Division of S61.NO. 815,044, April 10, 1969, and 6 3,366,722 1 1968 Tessier ..264/168continuation-in-part of Ser. No. 558,120, June 16, 19 66, abandoned.Primary Examiner-Jay H. W00 1 Attorney-Leonard Horn and Steven Murphy[52] US. Cl. ..264/l68, 264/171, 264/176 F,

, 264/177 F, 264/178 F, 264/210 F 57 ABSTRACT 51 1m. 01. ..D0ld 5/22[53] Field of Search 161/179, 181, 173 67, The present mvention relatesto a process for making 161/177; 264/167, 171-, 168, 178 F, 176 F, Y I21oF, 177F a flat-extruded yarn or ribbon of melt-extrudablethermoplastic material having a characteristic surface configuration,and to a method and apparatus for producing such yarn or ribbon.

11 Claims, 15 Drawing Figures PATENTEDFEB 6 I975 3.715.422 SHEET 1 or 4INVENTORS SOHINDER NATH CHOPRA HILAIRE MARCEL TURMEL ATTORNEYPATENTEDFEB 61875 3.715.422 SHEET 20F 4 SOHINDER NATH CHOPRA HILAIREMARCEL TURMEL ATTORNEY llwewrons' mgmgn 6 am 3.715.422

saw so; 4

N is 5 l 5/ 69? I V i r 744 K "67 INVENTO/PS SOHINDER NATH CHOPRAHILAIRE MARCEL TURMEL BY WW ATTORNEY mmmran 6 mm 3.715.422 sum u or 4SOHINDERINATH CHOPRA I HILAIRE MARCEL TURMEL ATTORNEY IIWENTORS lPROCESS FOR PRODUCING CRINKLED PLASTIC RIBBON This application is adivisional application of Ser. No.

815,044, filed Apr. 10, 1969, which is a continuationin-part applicationof Ser. No. 558,120, filed June 16,

1966, now abandoned. Flat-extruded yarn of melt-ex inch. Above thiswidth, more usually fromabout oneeighth inch width upwards, the wordribbon is more apt to describe the material. It is contemplated withinthe scope of the present invention to provide material of a width withina preferred range of about 0.0l inch to about one-quarter inch and withthis dimension in mind, the material will be referred to herein asflat-extruded yarn orribbon.

Conventional thermoplastic flat-extruded yarn or ribbon is generallyproduced by extruding a wide sheet and slitting such sheet into narrowwidths. It may also be produced by extruding the material through arelatively-narrow flat orifice. The continuous filamentary material thusproduced according to the known art is smooth and slippery. The materialhas little aesthetic or artistic appeal and suffers from the functionaldisadvantage that it is difficult to knot, and that crossing filamentsin a fabric containing the material tend to slip on the smooth surface.To avoid the latter disadvantage, flat yarn for use in fabrics issometimes crimped transversely by being passed through meshed gears orby being passed through a stuffer box. Crimping of this kind weakens thelengthwise stiffness or resiliency of the yarn and does not add to itsaesthetic appearance. I In accordance with one aspect of the presentinvention, there is provided a flat-extruded yarn or ribbonofthermoplastic material having two opposed faces, substantially straightand parallel side edges and an interior crimped region between the edgesin the form of a series of blister-like depressions and protrusions onboth faces.

The yarn or ribbon, in accordance with the process of theinvention,preferably has an overall width between the stated edges within therange of about 0.01 inch to about one-quarter inch, and a thicknessbetween the faces within the range of about 0.0005 inch to about 0.005inch. The length of the depressions and protrusions may lie within therange of'about onesixteenth inchto about one-eighth inch. Thedepressions and protrusions may be about 0.005 to 0.015 inch deep. Themelt-extrudable thermoplastic material is preferably selected from thegroup consisting of polyethylene, polypropylene, and polyacetal, and thepreferred material is polypropylene.

The yarn or ribbon in accordance with the invention combines artisticand aesthetic appeal with novel func? tional characteristics andadvantages. Since the surface deformations do not extend the whole wayacross the width of the yarn or ribbon, and since the blisters addadditional rigidity in the lengthwise direction to the used, forexample, for tying parcels and for similar purposes.

Yarn, in accordance with the invention in about the middle or towardsthe smaller part of the stated width range, finds application infabrics, especially carpet backing, for example, the type of carpetbacking described and claimed in our copending application, U.S. Ser.No. 498,389, filed Oct. 20, 1965, and now US. Pat. No. 3,443,541.

In accordance with a second aspect of the present invention, there isprovideda process for manufacturing a flat-extruded yarn orribbonofmelt-extrudable thermoplastic material having two opposed faces,substantially straight and parallel side edges and an interior crimpedregion between the edges in the form of a series of blister-likedepressions and protrusions on both faces, comprising the steps of:

yarn, the latter, exhibits an appreciable rigidity or ing a widthtowards the maximum of the stated range,

finds application as decorative material which may be melt extruding aflat yarn or ribbon having substantially a viscosity gradient settherein, from a melt extruder having ajet in the form of a slot andgenerating a substantial viscosity gradient,-

quenching the extruded yarn or ribbon to ambient temperature, and

stretching the cooled yarn or ribbon. Generally the stretching is doneby driving it under tension in contact against a convexedly curvedsurface heated at a temperature at or above the softening point andbelow the melting point of the said thermoplastic material, the yarn orribbon being taken up after stretching'at a faster speed than it is fedto the stretching surface.

Preferably, the temperature of the said curved surface is maintainedwithin the range of about C. to about C.

Having thus generally described the invention, it is hereafterillustrated by preferred embodiments of the yarn or ribbon, and ofapparatus for its manufacture, il-

lustrating the method of manufacture, which are described with referenceto the accompanying drawings, in which:

FIG. l is a greatly enlarged perspective view of a crinkled yarn orribbon in accordance with the invention;

FIG. 2 is a schematic representation of apparatus for the manufacture ofthe yarn or ribbon of FIG. 1, illustrating the method of manufacture;

FIG. 3 is a bottom plan view of a jet for the extruder forming part ofFIG. 2;

FIG. 3a is a section along the line 3a-3a of FIG. 3;

FIG. 4 is a vertical cross-section througha heating tube forming part ofthe apparatus;

FIG. 5 is a front elevation of the tube of FIG. 4;

FIG. 6 is a transverse cross-section along the line 6- 6 of FIG. 4;

FIG. 7 is a transverse cross-section along the line 7- 7 of FIG. 4;

FIG. 8 is a fragmentary perspective view on a large scale of the tube ofFIG. 4 partly assembled and showing its form of construction;

FIG. 9 is a transverse cross-section on a still larger scale along theline 99 of FIG. 8;

FIG. 10 is a greatly enlarged cross-section along the line 10-10 of FIG.5;

FIG. 11 is a greatly enlarged cross-section along the line 11-11ofFIG.5;

FIG. 12 is a side elevation on an enlarged scale of an automatic coolingand piling up mechanism;

FIG. 13 is a horizontal cross-section partly in elevation along the linel3 13 of FIG. 12; and

FIG. 14 is a diagrammatic view showing particularly the electricalcircuit for supplying current to the heating unit.

With reference to FIG. 1, there is shown a yarn or ribbon l ofpolypropylene having, for example, the width of 0.110 inch and athickness of, for example, 0.002 inch. The yarn exhibits a series, inalternating sequence, of blister-like protrusions 2 and depressions 3when viewed from the top face 4 as shown in FIG. 1. The number ofblisters per inch may vary between about 3 and about 10, the typicalribbon shown having, for example, 6 blisters per inch. The blisters varyin length from about one-sixteenth inch to one-eighth inch.

As shown, the yarn retains substantially straight and parallel sideedges 5, and the protrusions and depressions are restricted tosubstantially a central region. Occasionally, a blister will extend intoone or other side edge deforming that edge, and it is within the scopeof the invention that such occasional departures from the norm occur.

Over a greater part of the length at least, the straight edges 5 arecontinuous, and there is usually a flat edge portion 6 of each surfaceon either side of a blister-like protrusion or depression.

The transverse shoulders lying between a depression and the adjacentprotrusions add rigidity to the yarn or ribbon.

THE APPARATUS als having different intrinsic viscosity indices at agiven temperature, or preferably flows of an homogeneous moltenthermoplastic material, said flows having been subjected to differentheat treatment prior to extrusion at the spinneret orifice.

An example of extruder suitable for this purpose has been the subject ofU.S. Pat. No. 3,354,250 dated Nov. 21, 1967 owned by the same assignee,which was copending with our parent application Ser. No.

- 558,120. The said US. Pat. No. 3,354,250 is incorporated herein byreference.

As particularly seen from FIG. 10 and columns 6 and following of thesaid referenced patent, by the feeding screw S the polymeric materialreaches an aluminum block N having elongated passages 280. Bycontrolling the heat generated by the band heater 285, one is able tomake colder the material passing through the passages 280 located nearthe central axis of the block N, than the material passing through thepassages 280 located near the periphery of the block N or closer to theband heater 285. The molten material so treated is able to attain asubstantial viscosity gradient, and may then move through the remainingportion of the extrusion apparatus up to the spinneret orifice as asubstantial laminar flow (i.e., under such condition that the flow isnot homogeneized).

Other means may also be used to set a viscosity gradient, such asheating more intensively the innermost portion of the molten material.If necessary, cooling could be used instead of heating. Variation of theconcentration of the materials, or dilution, is also contemplated.

By substantial viscosity gradient it is meant that at the spinneret, theflat yarn or the ribbon obtained has a viscosity gradient which is suchthat after quenching and stretching, the flat yarn or ribbon will crimp.For example, it has been found that with polypropylene, if an apparatusas shown in FIG. 10 of US. Pat. No. 3,354,250 is used, the temperatureof the heating block should be maintained at a temperature between250300C and preferably 275-300C when the debit rate at the spinneretorifice is about 1 to 3% lbs. The spinneret being also maintained atabout that temperature or about 5-10C higher.

The extruder should terminate in a spinneret having a single jet orificein the form of a slot. A preferred jet is illustrated in FIGS. 3 and 3a.The plate 11 of the jet may typically have dimensions 0.465 inch thickby L996 total diameter. Typical dimensions of the slot 12 are 0.625 inchin length by 0.0 l 2 inch in thickness. The bottom of the jet has acentral dishing bounded by a conical surface 13. Tapped holes 14 areprovided for adjusting the orientation ofthe jet.

As the flat yarn or ribbon leaves the extruder, it is immediatelyquenched in running water at ambient temperature in the quencher 20. Asshown in FIG. 2, this consists of a generally U-shaped tube having aflared inlet 21 and a flared outlet 22 for the yarn and having aseparate water inlet 23 and a separate water outlet 24 in the side wallof the tube, the water inlet and outlet being arranged to provide acontinuous level of running water within the U-shaped tube. As shown,the quencher tube has a vertical limb at the input where the yarnenters, the outlet limb being at an angle to the vertical.

The ribbon leaves the outlet of the quenching device with its flat siderubbing against the lips of the outlet. This helps to drain back intothe quencher any water particles that may be riding on the ribbon. Asshown in H0. 2, the inlet to the quencher is arranged immediately belowthe extruder jet. In the preferred case, the distance between theextruder jet and the inlet of the quencher is only two inches. Thiscauses rapid cooling of the extruded ribbon or yarn. The bend of the Uof the quencher should be of sufficient radius to avoid undue strain onthe ribbon as it is being drawn around the convex inner surface andwhile it is being cooled. The radius of the U, for example, may be ofthe order of about four inches.

After passing out of the quencher, the yarn is passed over a first guideroll 201, and through a first pair of nip rolls 203 to a second guideroll 200 at the inlet of the heating tube R to be described. As itleaves the outlet of the stretching tube R, the yarn is passed through asecond pair of nip rolls 204 to a constant tension winder 40 ofconventional type.

Both the pairs of nip rolls 203 and 204 are driven, the nip rolls 204being driven at a faster speed than the nip rolls 203 so as to cause theyarn to stretch during its passage through the heat stretching tube RThe heat stretching tube R may be of the kind described in CanadianPatent 699,470. However, it is preferred to use a similar stretchingtube of improved construction described in our copending application asfollows:

U. S. Ser. No. 488,832, filed July 26, I965 now US. Pat. No. 3,277,228.

The improved stretching tube is shown in detail in FIGS. 4 to 14inclusive and incorporates a device for blowing air through the tube inthe event of fracture of the yarn or ribbon which would otherwise causethe tube to overheat. The blowing device is also an aid to threading theyarn or ribbon through the tube.

The tube or element R is made up of an elongated bowed trough or channelmember S, formed from a single sheet of electrically conductive metal ofthe shape shown in FIGS. 4 to 9. The trough S has a convexly curvedfloor 35 which preferably increases regularly in width from thereceiving end to the exit end and which 7 is bounded at each side by anupstanding integral flange or wall 37, which is of the same heightthroughout the length of the channel member S.

Against the outside of the trough so formed there is placed a glassfabric base laminate insulating strip 39 which lies on the top of walls37 and bridges the trough. The trough withthe strip 39 in place istightly wound with glass fiber tape 41 so as to form a four-sided tubeofwhich the floor 35 and walls 37 constitute three sides and the strip39 the other side.

The inlet end of the tube is provided with a copper terminal member 43having an opening 43a receiving the end of the tube and a connectingopening 43b. A threading nozzle in the form of a J-shaped tube 45extends through a diagonal opening 45a in the terminal member 43 andenters the bottom of the trough S at an angle as shown. The outlet endof the trough S is also provided with a copper terminal 47 having anopening sleeve 71 also has a part projecting outside the block 53. Theouter end of the sleeve 71 is internally threaded as at 71a to receivethe threaded end of a nipple 72 carrying at its outer end a bayonet cap74 held to it by a screw 74a. A thermocouple bulb 73 is positioned inthe sleeve 71 with an extension passing back through the cap 74. A coilspring 75 is mounted on the extension of the bulb 73 and acts between ashoulder 73a on the bulb and the cap 74 to urge the inner end of thebulb 73 against the wall of the trough S. The extension of the bulb 73leads to an instrument 163 (FIG. 14) where a reading may be taken of thetemperature sensed by the bulb 73.

47a receiving the end of the trough S and a connecting opening 47b. Theconnection between the metal part of the tube R and the terminals 43 and47 can be by welding, brazing, or any other suitable method. This alsoapplies to the connection between the tube and the plate 43.

The trough S is encased with insulation as follows. Elongated coatedjuxtaposed fiberglass blocks 51 and 53 are each provided with grooves 55and 57 respectively which form between them a channel receiving the tubeincluding the trough S, and its covering. The outer face of the block 51is clad with an aluminum facing sheet 65 and the block 53 is providedwith an aluminum facing sheet 67. The blocks 51 and 53 are clampedtogetherby non-magnetic screws 61 which extend through them and theircladding 65 and 67 periodically along the length of the heating elementR.

A thermocouple device V is connected to and extends through openings inthe facing sheet 65 and the block 53. This thermocouple has a base 69which is held by screws 70 to the sheeting 65 and its underlying block53. A sleeve 71 has a part whichextends through openings in the base 69,sheet 65 and block 53 to a point adjacent the outer surface of thetrough S. The

AUTOMATIC COOLING DEVICE The automatic cooling device K is best shown inFIGS. 12 and 13. This device includes a body which is mounted on a beam81 which extends along the length of the machine and also carries thesimilar stop motions for the other tubes R. The body 80 is of thecross-sectional shape shown in FIG. 13 and has a widened head 84projecting to one side and a widened foot 85 extending to the other sideand separated therefrom by a neck 86. The head 84 is provided with abore 87 extending through it from back to front and an inlet passage 88leading from a nipple 89 connected to an air inlet pipe 890. An outletpassage 91 extends from the bore 87 to a tee 93 connected to an air pipe94 leading to the cooling air connection 45. A piston 95 is operablymounted in the bore 87. The piston has an intermediate narrow part 97.The front of the piston is pivotally connected by a pin 98 through aslot in a link 99 which in turn is pivotally connected to a block 100mounting a drop wire 101. The block 100 is pivotally mounted on a bolt103 extending through the opening in the part 85. A stop bracket 104 ismounted on the back 86.

In operation, the drop wire 101 is in the upper position shown in dottedlines and is held in that position by the yarn under tension runningfrom the nip rolls 60 to the entrance of element R. In this position,the front thick part of the piston 95 blocks the outlet opening 91 andthus cuts off its supply of air from the inlet opening 88. When the yarnbreaks, the wire 101 is no longer supported and falls from the positionshown in full lines in FIG. 12. The fall is slow at first because thewire 101 is nearly vertical. The slot 99a has been provided in the link99 which acts an an elongated pivot hole thus allowing the wire 101 tofall freely through the first half of its travel, which developssufficient momentum to start the movement of the piston 94. The movementis completed during the second half of the travel. The fall of the wire101 pulls the piston 94 forward and clears the exit passage 91 thusallowing the air to pass through. it from the passage 88. The air isimmediately blown through the J connection 45 and into the tube R. Thisair serves to prevent the tube R from overheating when the yarn breaks.I

The apparatus is also provided with means for piecing up the yarn if itbreaks. This includes a compressed air pipe provided with a manual valve111. The valve 111 is connected by a pipe 112 to the tee 93 of thestretching unit. Through the tee 93 the pipe 112 is connected with thepipe 106 and thus with the J-connection 45. Byopening the valve 111compressed air is applied immediately to the .Lconnection 45 and throughthe trough S. The end to be fed is introduced into the end of the troughS carrying the stream of air, thus created, and is blown by it throughthe trough S from inlet to outlet. Once the new end of yarn is passedthrough the tube and onto the takeup rollers 29 and 30, the drop wire101 is reset by the operator into its normal upper position shown infull lines in FIG. 14 and the heating-stretching operation is continuedas previously described until there is another break.

Electric current is supplied through a transformer 151 by a wire 153through the terminal member 43 and connected by a wire 155 through theterminal member 147 (FIG. 14). The transformer is of suitable voltageand suitable amperage for heating the trough S to the desiredtemperature or a multiplicity of troughs in series or series parallel.The temperature may be controlled manually by means of a variablevoltage device 157. A thermocouple type of temperature-indicatinginstrument 163 may be connected to the thermocouple V by wire 165 so asto indicate the temperature of the trough S. The instrument 163 may beconnected into the electrical system so as automatically to regulate thetemperature, if desired.

If desired, a number of heating elements R may be provided on a singleframe to stretch yarn or ribbon from a corresponding number ofextruders. They may be connected in series on a single transformer.

The trough S is made preferably from stainless steel sheet in theannealed state, or chromel sheet, or nichrome, bent into trough shape.According to a preferred construction, it is polished to a mirror"finish on the inside or yarn guiding face then vapor blasted to aso-called satin" finish. This finish preferably consists ofirregularities approximately microns deep on the average, spaced in therange of to microns from peak to valley in all directions. After vaporblasting, the surface is provided with chromium plate, for example,about 0.002 inch thick. The irregularities may range from about 3microns to about 8 microns in depth and may be spaced within the rangeof about 10 to 50 microns (from center to center). Where the surface ofthe trough S has been treated to reduce friction, as described, thecurvature ofthe trough S is not critical.

Such a surface may be prepared by first polishing the metal surface to amirror-like finish. Then blasting with a fine abrasive powder carried ina stream of air and water vapor at high velocity. This provides thesurface with a multitude of microscopic indentations. The thus preparedsurface is then chromium-plated. The resulting chromium-plated surfacereduces the frictional resistance of thesurface to the yarnsubstantially to a minimum and prevents wear. For a surface of thisnature, the curvature is not critical, whereas, without such afriction-free surface, it is desirable'that the curvature of the surfacebe such that it is relatively less curved at the inlet end to reduce thefriction and it is more curved towards the outlet end, so as to providea certain amount of friction. Thus, at the inlet end, the yarn or ribbonis not subjected to any substantial friction, and thus is not stretchedbefore it is sufficiently softened, while towards the outlet end it issoftened and is then subjected to friction and stretched. With thechromium-plated surface as described, the resistance offered to the yarnor ribbon is at a minimum and consequently, the curvature being muchless critical, the stretching trough may be curved to suit a particularassembly or machine to provide a convenient location at the inlet andoutlet for ease of operation.

The length of element R may be adapted to suit the machine, with thelength about as long as practical without exceeding the maximum reach ofthe average operator. Shorter lengths can be used, but the speed ofstretching would have to be reduced accordingly. If the length of thetube is increased, maintaining the same radius, the machine would haveto be higher. If the radius is decreased maintaining the same length,the tube would project further out the back and occupy more floor space.

The radius of the trough S may vary from inlet to outlet with themaximum radius at the inlet and the minimum radius at the outlet. Thesurface may take a single curve or a series of curves of varying radii.The greater the curvature, the greater the tension on the yarn. Theideal curvature maintains contact of the surface with the yarn but isinsufficient to cause drag or high friction. Preferably, the radius ofthe curvature of the trough S should remain within about 24 inches andabout 40 inches and may vary in curvature along the length with theshort radius preferably at the outlet end. A practical length is betweenabout 4 feet and 8 feet, it being understood that when the tube isshorter, the stretching speed would be reduced.

A preferred overall length is about 6 feet from terminal to terminal,bent into an arc comprising 128)? of a circle. This shape of tubeprovides suitable pressure ofthe yarn against the running surface andthe length is sufficient for ordinary rates of stretching. A typicaltrough-shaped heating element having a length of 72 inches through thefirst 68 W ofits curvature and then a radius of curvature of about 30inches for the last 60 of its curvature with a transition between thesetwo radii of curvature in between.

Theoretically, the thickness of the metal wall of the trough can varyconsiderably. The thicker the wall, the more amperage is required intheory, the tube could be as thin as about l/64 inch, but it would notbe self-supporting. It is preferred that the metal wall of the trough bein the neighborhood of one-sixteenth inch, when constructed as shown.

A preferred metal for the manufacture of the trough S is an alloy ofnickel and chrome, available on the market under the trade marks CHROMELand NlCHROME. These metals are ideal since they have high electricalresistance, sufficient heat conductivity and are free from oxidationwhen operated at high temperatures. Most of the chrome-nickel stainlesssteel alloys, although of lower electrical resistance, are also suitableand are readily available for tube forming. The amperage used forheating must be adjusted in accordance with the resistivity of the metalused and the thickness of the wall.

The amperage used for heating may be varied to suit the composition ofyarn or ribbon and dimensions being stretched. The temperature of thetrough must be adjusted to heat the yarn or ribbon to its softeningpoint. The exact temperature will vary with different types of yarn. Forpolypropylene, for example, the temperature is preferably within therange from about Extrusion temperature 115C. to about 155C. measured atthe surface of the ple, cylindrical, D-shaped, etc. The surface of theconformation described, however, has decided advantages, and it istherefore greatly preferred.

It may be desirable to pass the yarn or ribbon through several tubes inseries with a pully between them to the necessary longer residence timeat higher speeds and higher stretch ratios. The tubes are normallyconnected in series electrically but can be connected in parallel or inany series-parallel combination. In all cases, they should preferably becalibrated so that their respective electrical resistances areidentical.

The tape with which the trough S is wrapped may be plain woven glassfabric completely dry with no adhesive and coated with shellac, phenolresin, or other suitable adhesive.

The ratio of input speed to output speed may vary widely for differenttypes of yarn or ribbon, but a preferred stretch range is between threeand six times the extruded length.

The winder 40 and the drive rolls 60,61 are preferably adjustable inspeed to accommodate different stretch ratios ranging from 3:1 to 12:1and for different speeds, the element R being adjustable to differenttemperatures, making the apparatus suitable for a wide range ofdifferent polymers.

The tension in yarn as it leaves the final heating zone is determined bythe force required for stretching at the optimum stretching temperature.The tension in the yarn as it enters the heating element equals thestretching tension minus the force required to overcome the frictioncaused by the yarn sliding on the surface. The curvature and length andtemperature of the tube is designed so that the tension on the yarn doesnot increase to the stretching tension until the yarn has been heated tooptimum stretching temperature. The optimum temperature varies inrelation to the dimensions of the vyarn or ribbon, stretch ratio, speedand the viscosity of the parent polymer, but generally it is in therange ofabout 100C. to about 135 EXAMPLE A polypropylene ribbon was meltextruded using following extrusion conditions were used:

270C. 1% lbs. per hour 55 feet per minute Extrusion output Extrusionspeed Cooling water temperature Distance of water level from jet face 2inches Jet orifice 0.012 inefx' as inch X 14 inch deep Temperature ofstretching surface 120C. Stretch ratio 4-511 Ribbon size 1100 denier,0.002 inch thick X 0.1 10inch wide parent thickness of the ribbon wastherefore 0.021 inch.

We claim: l. A process for manufacturing a flat-extruded yarn or ribbonof melt-extrudable thermoplastic material having two opposed faces,substantially straight and parallel side edges, the overall widthbetween said edges being within the range of about 0.01 inch to aboutone-quarter inch and an interior crimped region between the edges in theform ofa series of blister-like depressions and protrusions'on bothfaces, the length of said depressions and protrusions lying within therange of about one-sixteenth inch to about one-eighth inch and the depthof said depressions and protrusions lying within the range of about0.005 inch to 0.015 inch, comprising the steps of:

melt extruding a flat yarn or ribbon having a substantial viscositygradient set therein from a melt extruder having a jet in the form of aslot and generating a substantial viscosity gradient,

quenching the extruded yarn or ribbon with water to ambient temperature,and heat stretching the cooled yarn or ribbon at a temperature at orabove the softening point and below the melting point of the saidthermoplastic material.

2. A method as claimed in claim 1 wherein said stretching is obtained bydriving said cooled yarn or ribbon under tension in contact against aconvexedly curved surface heated at a temperature at or above thesoftening point and below the melting point of the said thermoplasticmaterial, the yarn or ribbon being taken up after stretching at a fasterspeed than it is fed to the stretching surface.

3. A method as claimed in claim 2 wherein the temperature of the saidcurved surface is maintained within the range of about C. to about 160C.

4. A method as claimed in claim 3 wherein the said thermoplasticmaterial is polypropylene.

5. A method as claimed in claim 4 wherein the temperature of the saidcurved surface is maintained at about C.

6. A method as claimed in claim 7 wherein the extruded yarn or ribbon isquenched in a liquid at ambient temperature.

7. A method as claimed in claim 6 wherein the extruded yarn or ribbon isquenched by being continuously passed through a tube through which waterat ambient temperature is continuously passed.

8. A method as claimed in claim 1 wherein the yarn or ribbon isstretched between about three and about 1 six times its extruded length.

9. A method as claimed in claim 5 wherein the, extruded yarn or ribbonis quenched by being continuously passed through a tube through whichwater at ambient temperature is continuously passed, and the yarn isstretched about 4% times its original extruded length.

10. A method as claimed in claim 2 wherein the said curved surface isone side of a heated tube whereby the yarn is heated on'all sides.

11. A method as claimed in claim 2 wherein the said curved surface isone side of a heated tube whereby the yarn is heated on all sides, andwherein the length of the tube is between about 4' and about 8 feet, theradius being sufficient to maintain contact of the yarn or ribbonagainst the convex surface without causing drag or high friction.

1. A process for manufacturing a flat-extruded yarn or ribbon ofmelt-extrudable thermoplastic material having two opposed faces,substantially straight and parallel side edges, the overall widthbetween said edges being within the range of about 0.01 inch to aboutone-quarter inch and an interior crimped region between the edges in theform of a series of blister-like depressions and protrusions on bothfaces, the length of said depressions and protrusions lying within therange of about one-sixteenth inch to about one-eighth inch and the depthof said depressions and protrusions lying within the range of about0.005 inch to 0.015 inch, comprising the steps of: melt extruding a flatyarn or ribbon having a substantial viscosity gradient set therein froma melt extruder having a jet in the form of a slot and generating asubstantial viscosity gradient, quenching the extruded yarn or ribbonwith water to ambient temperature, and heat stretching the cooled yarnor ribbon at a temperature at or above the softening point and below themelting point of the said thermoplastic material.
 2. A method as claimedin claim 1 wherein said stretching is obtained by driving said cooledyarn or ribbon under tension in contact against a convexedly curvedsurface heated at a temperature at or above the softening point andbelow the melting point of the said thermoplastic material, the yarn orribbon being taken up after stretching at a faster speed than it is fedto the stretching surface.
 3. A method as claimed in claim 2 wherein thetemperature of the said curved surface is maintained within the range ofabout 100*C. to about 160*C.
 4. A method as claimed in claim 3 whereinthe said thermoplastic material is polypropylene.
 5. A method as claimedin claim 4 wherein the temperature of the said curved surface ismaintained at about 120*C.
 6. A method as claimed in claim 7 wherein theextruded yarn or ribbon is quenched in a liquid at ambient temperature.7. A method as claimed in claim 6 wherein the extruded yarn or ribbon isquenched by being continuously passed through a tube through which waterat ambient temperature is continuously passed.
 8. A method as claimed inclaim 1 wherein the yarn or ribbon is stretched between about three andabout six times its extruded length.
 9. A method as claimed in claim 5wherein the extruded yarn or ribbon is quenched by being continuouslypassed through a tube through which water at ambient temperature iscontinuously passed, and the yarn is stretched about 4 1/2 times itsoriginal extruded length.
 10. A method as claimed in claim 2 wherein thesaid curved surface is one side of a heated tube whereby the yarn isheated on all sides.